One technique for cutting or grooving metal is to rotate the workpiece (for example, by fixing the workpiece in a rotating workholder or chuck) and advance a rigid cutting edge against the workpiece. A preferred form of cutting tool for this purpose comprises a rigid support blade which mounts a removable cutting insert which acts as the cutting edge of the tool.
In order to avoid excessive down time during the replacement of a worn insert, it is desirable that the insert be mounted on the support blade so that the insert may be removed again quickly and easily. One popular style of mounting uses so-called "self-gripping" inserts, which frictionally engage a recess in a forward end of the support blade without additional fasteners.
A drawback to the use of self-gripping inserts is that the accuracy of the cut may be difficult to control. One conventional design for support blades has an insert-receiving recess that tapers linearly inward from the front edge and terminates in a circular aperture that minimizes stress concentrations on the inner surface of the recess and facilitates the removal of the insert. When the insert is pressed against a workpiece, the reaction from the workpiece tends to push the insert farther back into the workpiece. Since the depth and center-line of the cut are determined relative to the insert as seated in the blade prior to cutting, the accuracy of the depth and center-line may be difficult to control over an extended production run.
One advantage of the conventional insert and support blade design with a tapered recess terminating in a circular aperture is ease of removal of the insert. In order to remove the insert, a camming tool is introduced into the aperture at the back of the insert-receiving recess and turned. One side of the camming tool engages the back of the aperture while the other side engages a flat back face of the insert to push the insert forward out of the recess.
Even this advantage may be neutralized by movement of the insert into the blade during cutting. If the insert is pushed sufficiently far back into the insert-receiving recess during a production run, it may become difficult to introduce the camming tool into the aperture behind the insert in order to remove the insert from the blade.
Various approaches have been used to more positively position a self-gripping insert in its recess, as by providing a rearwardly facing surface on the insert and a forwardly facing surface adjacent the recess arranged so the two surfaces abut and positively limit movement of the insert into the recess. In particular, one popular insert design provides a rearwardly facing surface near the back of the upper chip forming or breaking surface of the insert which abuts against the upper lip of the recess to limit movement of the insert into the blade. Another conventional design provides a narrow projection from the back of the recess which abuts against a back surface of the insert. Neither of these solutions provides an optimal degree of support against rearward movement of the insert.
Many conventionally designed inserts have flat rear surfaces facing the aperture into which the camming tool is introduced. Since the rear surface is flat, the camming tool may be turned either clockwise or counter-clockwise to remove the insert from the blade.